The operating data for a ball mill is summarized;

Mill dimensions $($inside liners$)=1\mathrm{.}6$m $($diameter$)$ by $3\mathrm{.}2$m

Mill speed $=25$ rpm

Pulp density in mill $=84\%$ solids

Total solids exiting mill $=40$ tph $($dry$)$

Solids $($ore$)$ specific gravity $=2\mathrm{.}8$

Steel ball charge $=43\%$

Density of steel ball $=7\mathrm{.}8$ t$/$m$3$

Steel void space $=39\%$

Express the mill speed as a percentage of the critical speed. $(4)$

Calculate the steel ball charge for such an empty mill in tonnes. $(4)$

Express the mill pulp density in terms of;

Liquid$-$Solid ratio $($dilution ratio$)(3)$

tonnes$/$m$3(3)$

Compute the mill feed water addition if mill feed contains $1\mathrm{.}6\%$ moisture. $(4)$

Indicate the purpose of mill liners. $(3)$

Calculate the rate of ball addition $($balls per hour$)$ if steel balls of diameter $75$mm are used and consumption rate being $1\mathrm{.}02$ kg$/$t of ore. $(4)$